Abstract

When NAPDH was added in excess to a bovine liver DHFR solution, a fluorescence peak due to an energy transfer mechanism was apparent at 450 nm. It did not vary over time. The intrinsic fluouresence peak of DHFR at 320 nm was quenched and this phenomenon increased over the time-course after NADPH addition. This result was ascribed to a slow DHFR conformational change induced by NAPDH binding, which has never been previously described in such a long time scale (more than 30 min). A kinetic scheme accounting for this mechanism has been proposed. Furthermore, this interconversion between two protein conformers led to an increase in the initial apparent rate of enzymatic reaction catalyzed by DHFR.

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